Prostate cancer cells, like normal prostate secretory-luminal epithelial cells, produce very high levels of the PSA. PSA is aptly named, in that it is produced at high levels exclusively by prostate cells and is not produced in significant amounts by any other normal tissue in the human male. PSA is a chymotrypsin-like serjne protease that is used extensively as a biomarker to screen for prostate cancer, to detect recurrence following local therapies and to follow response to systemic therapies for metastatic disease. PSA, however, is also a well credentialed therapeutic target for prostate cancer. The focus on PSA's role as a biomarker has made perhaps made